Cocoon-to-Butterfly Transformation in Protoplanetary Nebula: Detection of a Spherical Halo and a Barrel-shaped Torus in IRAS 06530$-$0213

Hao-Min Sun, Yong Zhang, Sheng-Li Qin

Protoplanetary nebulae (PPNs) represent a critical evolutionary bridging stage between the asymptotic giant branch (AGB) and planetary nebula (PN) stages. Their dynamical structure…